Answer
Choice A.
Work Step by Step
Find the energy from the wavelength.
For a nonrelativistic ion, $E=\frac{p^2}{2m}=\frac{h^2}{2m\lambda^2}$.
$$E=\frac{(6.626\times10^{-34}J \cdot s)^2}{2(7300)(9.11\times10^{-31}kg)(0.1\times10^{-12}m)^2}$$
$$E= 3.3\times10^{-15}J=2.1\times10^4 eV$$
We see that the voltage required is 21 kV.
